Rare genetic variants with large effect on triglycerides in subjects with a clinical diagnosis of familial vs nonfamilial hypertriglyceridemia.

BACKGROUND: Most primary severe hypertriglyceridemias (HTGs) are diagnosed in adults, but their molecular foundations have not been completely elucidated. OBJECTIVE: We aimed to identify rare dysfunctional mutations in genes encoding regulators of lipoprotein lipase (LPL) function in patients with familial and non-familial primary HTG. METHODS: We sequenced promoters, exons, and exon-intron boundaries of LPL, APOA5, LMF1, and GPIHBP1 in 118 patients with severe primary HTG (triglycerides >500 mg/dL) and 53 normolipidemic controls. Variant functionality was analyzed using predictive software and functional assays for mutations in regulatory regions. RESULTS: We identified 29 rare variants, 10 of which had not been previously described: c.(-16A>G), c.(1018+2G>A), and p.(His80Arg) in LPL; p.(Arg143Alafs*57) in APOA5; p.(Val140Ile), p.(Leu235Ile), p.(Lys520*), and p.(Leu552Arg) in LMF1; and c.(-83G>A) and c.(-192A>G) in GPIHBP1. The c.(1018+2G>A) variant led to deletion of exon 6 in LPL cDNA, whereas the c.(-16A>G) analysis showed differences in the affinity for nuclear proteins. Overall, 20 (17.0%) of the patients carried at least one allele with a rare pathogenic variant in LPL, APOA5, LMF1, or GPIHBP1. The presence of a rare pathogenic variant was not associated with lipid values, family history of HTG, clinical diagnosis, or previous pancreatitis. CONCLUSIONS: Less than one in five subjects with triglycerides >500 mg/dL and no major secondary cause for HTG may carry a rare pathogenic mutation in LPL, APOA5, LMF1, or GPIHBP1. The presence of a rare pathogenic variant is not associated with a differential phenotype.

MAPK and PI3K activities are required for leptin stimulation of protein synthesis in human trophoblastic cells.

Leptin, the LEP gene product, is produced in placenta where it has been found to be an important autocrine signal for trophoblastic growth during pregnancy. Thus, we have recently described the antiapoptotic and trophic effect of leptin on choriocarcinoma cell line JEG-3, stimulating DNA and protein synthesis. We have also demonstrated the presence of leptin receptor and leptin signaling in normal human trophoblastic cells, activating JAK-STAT, PI3K and MAPK pathways. In the present work we have employed dominant negative forms of MAPK and PKB constructs to find out the signaling pathways that specifically mediates the effect of leptin on protein synthesis. As previously shown, leptin stimulates protein synthesis as assessed by (3)H-leucine incorporation. However, both dominant negative forms of MAPK and PKB inhibited protein synthesis in JEG-3 choriocarcinoma cells. The inhibition of PKB and MAPK activity by transfection with the dominant negative kinases prevented the leptin stimulation of p70 S6K, which is known to be an important kinase in the regulation of protein synthesis. Moreover, leptin stimulation of phosphorylation of EIF4EBP1 and EIF4E, which allows the initiation of translation was also prevented by MAPK and PI3K dominant negative constructs. Therefore, these results demonstrate that both PI3K and MAPK are necessary to observe the effect of leptin signaling that mediates protein synthesis in choriocarcinoma cells JEG-3.